I understand that perhaps for speed that exiftool stops parsing at the first cluster; however as mkv is a fairly editable format, often chapters and tags are found at the end of the file.

Here are two samples:
tags_after_clusters.mkv.zip
tags_before_clusters.mkv.zip

With exiftool tags_before_clusters.mkv I can see the embedded metadata

Tag 1                           : value1
Tag 2                           : value2
Willtest                        : in_exiftool

but not in exiftool tags_after_clusters.mkv. I've been using -ee as a workaround, but I think the tags element is pretty critical to a matroska file and if its position is clarified by the SeekHead so a parser doesn't need to do a long search for it, then I'd suggest including it in a preliminary parse on default.

Thanks